HEATER PA-28 151

The heater on my warrior does not seem to be working. The defrost works bur when i slide the heater lever, no heat comes out. checked the flapper valve and it works, also made sure the floor vents are open. Any Ideas

If the flapper is working correctly and the defroster is working, there must be a blockage in the ducting aft of the control. I suggest you get a strong flashlight and an inspection mirror to look inside the ducting to see of a creature decided to move in and build a nest.
If your mechanic has a borescope that will help view the inside of the heat ducting.
Please take pictures and let me know what you find.